Process and product of zinc and aluminum lamination



States Patent 2,987,814 PROCESS AND PRODUCT F ZINC AND ALUMINUM LAMINATION Ogle R. Singleton, 11:, Richmond, and George E. Stein, Henrico County, Va., assignors to Reynolds Metals Company, Richmond, Va., a corporation of Delaware No Drawing. Filed Jan. 25, 1957, Ser. No. 636,232

12 Claims. (Cl. 29-4723) This invention relates to improvements in cladding of aluminum with zinc or zinc alloys.

In accordance with the novel method of the present invention, aluminum cores clad with zinc or other solderable metal may be obtained, starting from the ingot stage, by a simplified and economical procedure. The new method assures a substantially uniform and firm bond between the aluminum and the cladding metal, to provide a clad aluminum having good formability, mechanical properties, and corrosion characteristics. The clad product may be used as a replacement for such materials as copper or brass or galvanized iron in applications in which solderability is of importance. In such applications, it may be soldered using conventional equipment and techniques, and avoiding the special solders and fluxes, equipment, and controls heretofore necessary in soldering aluminum.

Previous methods of uniting aluminum with laminations of' other metals by mechanical means, as distinguished from chemical or electro-deposition, have generally been basedupon the use of an intermediate layer of aluminum foil or alloy to serve as a bonding agent between the coating metal and the aluminum core. It is known, for example, tobond a copper-base cladding metal to aluminum strip, slabs or ingots by means of a preliminary rolling of the copper-base metal with aluminum foil, followed by a second rolling at raised temperatures to effect a bond with the aluminum core. In another known method, aluminum is applied as a surfacing metal on zinc by means of an intermediate bonding layer of zinc-aluminum alloy. In yet another known method, other metals are bonded to aluminum by cold rolling using as much as a 60 percent reduction in a single pass. For practical purposes, these prior art meth- 'ods are confined to the production of relatively thin sheets or foils from thin cores and liners.

For the purpose of imparting solderability, it has .hitherto-been the practice to coat aluminum with zinc or tin by' brushing the molten zinc or tin onto the surface of the heated aluminum with wire brushes to form a surface alloy. These methods are laborious and the surface alloys penetrate into the aluminum to a greater extent than is desirable, and with adverse effects upon the ductility of the aluminum.

- In accordance with the present invention, an aluminum core is clad with Zinc or a zinc alloy containing less than 1% by weight of alloying metals which have a melting point below that of pure zinc (about 786 F.), when'the claddingis applied to only one side of the core, and less than 0.02% of said low melting metals when the cladding is applied to both sides of the core. The said limit on low melting metals is necessary to avoid hot shortness.

A greater amount of alloying metals having a melting point higher than zinc is permissible, e.g., 0.5% by weight of copper in the alloy, because the high melting point is a safeguard against hot shortness. However, other factors, such as corrosion, make it advisable to limit: the amount of alloying metals of all kinds as far as practicable. For the best and most consistently good results in practicing the invention, the zinc liner preferably contains not more than 0.01% by weight of nonzinc materials, particularly whereadouble liner is applied.

2,987,814 Patented June 13, 196} ICC 2 Where a single liner is applied, the zinc may have a larger proportion of impurities, e.g., 0.36% lead, 0.27% cadmium and 0.019% iron, the balance of 99.351% being zinc.

The cladding metal layer or layers are first placed in contact with the aluminum core to form an assembled composite. This composite is then heated to a temperature slightly below the melting temperature of the cladding metal. If there is any tendency toward the formation of a eutectic alloy between the cladding metal and the aluminum, the heating temperature is preferably kept slightly below the melting temperature of such eutectic alloy. The heated composite of cladding metal and aluminum core is then rolled lightly several times, using a very small reduction per pass, to effect adhesion 0r sticking'of the cladding layer to the core. The composite is then hot rolled in accordance with normal aluminum hot rolling'practice, using as large a reduction per pass as practicable, until the desired hot line gauge is obtained. The clad aluminum may be further cold rolled in accordance with customary aluminum rolling practice to any desired gauge, with or without intermediate annealing.

The novel method of this invention makes possible in the form of ingots or slabs ranging in thickness from one inch up to one foot or greater, and of cladding metal layers as much as one inch or more in thickness. It is within the contemplation of the invention to provide the cladding on one or both faces of the core, or on a portion of one or both faces. The new method thus provides for production of heavier gauges of clad aluminum, and improved economy of production of lighter gauges of clad aluminum;

Pure zinc is generally regarded as the most corrosion resistant soldering metal for joining aluminum, but has notvbeen widely adopted for this purpose owing to its poor flow properties; Cladding pure zinc to aluminum, however, is equivalent to a preplacing of the solder, and thus eliminates the need for high flowability requirements. Such zinc cladding not only provides a solderable surface, but when the coating is of suflicient thickness, the zinc itself acts as a solder.

In order to clad aluminum with zinc in accordance with the present invention as previously outlined, careful attention must be given to several factors.

The requirements as to the constitution of the zinc layer or liner have been stated above.

The surface of thezinc liner to be bonded is cleaned prior to use by removal of the oily or wax coating in which it is customarily shipped, preferably with kerosene or other solvent. The surface of the aluminum core to be bonded is also cleaned before use, preferably by scalping.

Another factor of importance in carrying out the novel method of this invention is regulation of the temperature and time of preheating of the composite of cladding metal layer and aluminum core. In the preparation of this composite, the aluminum core may be, for example, a direct chilled cast ingot of aluminum or of aluminum alloy. The alloying elements with the aluminum are not critical for the purposes of the invention, and are preferably present in total amounts not over about 1% by In general, the softer the cladding metal and the aluminum. Zinc and aluminum 3 are known to form a eutectic containing about 96 percent of zinc and having a melting point of approximately 720 F. The melting point of pure zinc is about 786 F. Accordingly, in cladding zinc on aluminum by the method of this invention, it has been found that the preheating step is best carried out in a temperature range of about 650 F. to 750 F., and preferably between about 650 F. and a temperature below 720 F. Avoidance of eutectic formation is of importance because the molteneutectic acts as a lubricant and retards adherence of the zinc to the aluminum core, especially where larger sized composites are being processed. The lower limit of approximately 650 F. will ordinarily bev found to be the lowest practicable temperature in order'to avoid difficulties arising from working colder metal. However, the temperature range selected in any given instance will also depend upon the properties of the aluminum or aluminum allow used for the core.

While the composite of cladding metal and aluminum core may be heated in any suitable manner, the invention permits heating in any ordinary furnace using no special atmosphere. Thus, for example, a recirculating air type furnace may be used for heating the composite to the desired temperature.

The zinc or other cladding plates may be temporarily attached to the aluminum core with suitable fastening means, such as steel bands, or baling wire. The presence of the zinc plates serves as a cover for the core and keeps oxide film formation under these oxidizing conditions to a minimum. It also enables the hot composite to be transfered through the atmosphere to the hot rolling mill for the next operation Without adverse effects on bonding. Complete support for the lower zinc liner is desirable to prevent sagging at these temperatures.

The time of preheating of the zinc-aluminum composite will depend upon its dimensions, and may vary from 2 or 3 hours up to 13 or 14 hours for larger sizes. In any event, best results are obtained by rolling as soon as possible after the metal has reached the desired temperature.

Following the preheating, the composite is taken from the furnace, the fastenings are removed, and the composite is then subjected to hot rolling, using little or no lubrication for a suflicient number of very light successive reductions (about one quarater of the reduction per pass normally practiced in cladding aluminum), to cause the zinc layer to adhere to the aluminum core. Reductions of about 0.003 to about 0.015 inches per pass have been found to be adequate for the purpose when rolling relatively small composites in correspondingly small mills (e.g., inch roll length), and about 0.005 to about 0.05 inches when rolling relatively large composites in correspondingly large mills (e.g., l20inch roll length). Depending upon the size of the composite, the number of passes may vary from 2 or 3 up to 30 or 40. These small successive reductions are to.be made at a pressure sufiicient to cause adhesion or sticking of the zinc layer, but not so great that the liner will curl or peel away from the core. Other methods suitable for preventing liner curl or peel are also known. to those skilled in the art.

After the adhesion passes, the composite is subjected to heavy reductions in the hot mill, using conventional aluminumhot rolling practice, such as, for example, hot rolling to 0.35 inch plates and subsequently to hot line gauges of 0.25 to 0.10 inches. The hot rolling temperatures gradually decreased from the preheating temperatures, because the mechanical heating effect of the rolling does not entirely make up for loss of heat by radiation and convection, and the rolling temperature may be lowered to about 400 F. at final hot line thickness. The hot' rolling may be conducted in the atmosphere of standard mills.

The hot line gauge material may be finished to any desired gauge by'regular'cold rollingmethods, depending uponthe gauge andtemperdesired:

As aluminum core material, ingots or slabs of any suitable aluminum alloy may be used, such as, for example, the alloys corresponding to the following Aluminum Association Alloy Designations: 1100, 1175, 3003, 5005, and 7072, and an experimental alloy of 96% by weight of 1175 aluminum alloy and 4% zinc.

The method of this invention is capable of producing zinc clad aluminum having excellent solderability, formability, and corrosion characteristics, and exhibiting a substantially uniform and firm intermetallic bond between the two metals.

The properties of the final product may be varied in accordance with the relative thickness of zinc cladding employed. This thickness may range, for example, from about 3 to 10 percent of the over-all thickness of the composite, using a single liner. Thus, a zinc liner of 0.2 to 0.6 inches thickness may be applied to one or both sides of an aluminum ingot approximately 2.5 inches thick. On a larger scale, an ingot about 11 inches thick may be combined with one or two zinc plates each about one inch thick, to form a cladding composite. These types of composites may then be rolled, for example, to an over-all, thickness of 0.006 inch of which 0.0004 inch is zinc (half on each side) and 0.0056- inch is aluminum core, or to an over-all thickness of 0.012 inch of which 0.0012 inch is zinc (half on each side) and 0.0108 inch is aluminum core.

Where, for example, the thickness of the zinc coat in the final sheet is about 0.0004 inch, the product possesses a surface solderable with conventional solders. If the zinc coating in the final sheet is greater than about 0.001 inch in thickness, the coating is not only solderable, but is itself solder furnishing. The effect of zinc liner thickness on solderability of zinc clad aluminum sheet is seen from the following Table 1:

TABLE I Solderability of aluminum clad with zinc in accordance with the invention Percent Calculated Sheet of Zinc Zinc Thickness Cladding Thickness Solderability (Inches) Liner to (Mils) Composite 6 0. 36 Continuous coating, solderable. 3 0.36 Do. 6 0.72 Continuous coating, solderable and slightly solder furnishing. 10 1.20 Coating solder furnishing.

The following examples illustrate the practice of the invention.

EXAMPLE 1 A direct chilled cast ingot ofaluminum alloy 1175 (99.75% minimum aluminum content) is scalped to provide a core approximately 2.15 inches thick, 8 inches wide and 20 inches long, and wiped to remove oil or grease. Two liners of high purity zinc (at least 99.99% zinc content) and each about 0.3 inch thick are wiped with rags soaked with kerosene to remove the lardparaflin coating in which they were shipped, and then wired to each face of the ingot to form a composite. The composite is heated in a recirculating air furnace from 2 to 4 hours at a furnace temperature within the range 650 F. to 750 F. The heated composite istaken from the furnace, placed on the rolling table, the wires removed, and then given about three light rolling passes ('20 inch roll length) with reductions of approximately 0.01 inch each to cause the liner to adhere to the core. Conventional aluminum hot rolling practice is then followedto a hot line gauge of 0.25 inch with no rolllubrication.

per, not more than 0.01% of materials other than zinc and copper, and the balance zinc, and an ingot of 7072 aluminum alloy (0.7% silicon and iron, 0.10% copper, 0.10% magnesium, from 0.8 to 1.3% zinc, and the balance aluminum), is prepared, heated (at about 715 F.) and rolled, as described in the case of Example 1.

EXAMPLE 3 A composite of two high purity zinc liners and an ingot of 1175 aluminum alloy is prepared as described in pre ceding Example 1, and heated for three hours in a recirculating air furnace at a temperature within the range 650 F. to 720 F. The composite is then given three sticking passes (each about 0.05 inch reduction) and hot rolled to 0.25 inch gauge. The composite strip is then cold rolled to a sheet gauge of 0.006 inch.

EXAMPLE 4 An ingot of aluminum alloy 7072 which is 12 inches thick, 40 inches wide and 70 inches long is scalped to a thickness of 8 to 12 inches. After first being cleaned with kerosene-soaked rags, two high purity (99.99%) zinc liners each one inch in thickness are attached to the upper and lower faces of the aluminum core with steel bands. The composite is heated in an air furnace at a temperature in the range 680 F. to 700 F. for 13 hours. The steel bands are removed and the hot composite subjected to 12 sticking passes on the hot rolls (120 inches long), using very small reductions of about 0.01 inch per pass, initially, and increasing to about 0.05 inch per pass, with little or no lubrication. Conventional aluminum hot rolling procedures are then used to reduce the clad material to a hot line gauge of 0.25 inch. A plurality of passes on cold rolls further reduce the material to the desired finish gauge.

EXAM'PLE 5 A composite of liners of 15% aluminum and the balance high purity (at least 99.99%) zinc, and an ingot of 1175 aluminum, is prepared, heated (at about 700 F.) and rolled, as described in the case of Example 1.

EXABIPLE 6 An ingot of aluminum alloy 1100 (nominal composition 99.0% aluminum content) of 12 inch thickness and approximately 100 inch length and 40 inch width, is scalped to a thickness of 8 inches. After first being cleaned with kerosene-soaked rags, two high purity (99.99%) zinc liners each 0.55 inch in thickness are attached to the upper and lower surfaces of the aluminum ingot core. The attachment is elfected with steel bands. The composite is heated in an air furnace at a temperature in the range of 680 F. to 700 F. for about 13 hours. The steel bands are removed and the hot composite is then subjected to about 15 sticking passes on a hot mill (120 inch roll length) using very small reductions per pass (initially about 0.01 inch per pass, and increasing to about 0.05 inch), and employing some cross rolling. Then normal hot rolling procedures are employed reducing the final hot line thickness of the zinc aluminum composite to about 0.150 inch.

The clad aluminum produced in accordance with each of the above examples has a continuous zinc coating which presents a solderable surface and provides a layer of zinc to supply the solder.

While we have illustrated and described present preferred embodiments of the invention, and methods of the heated composite to adhere the zinc plate to the aluminum ingot, and then hot rolling the adhered composite under pressure to reduce the thickness of the composite and to bond the zinc plate to the aluminum ingot, said zinc plate containing not more than a minor proportion by weight of alloying metals having a melting point higher than zinc, less than about 1% of metals having a melting point lower than zinc, the balance being 21m.

2. The method of claim 1 in which the composite is cold rolled after the hot rolling operation to further reduce the composite.

3. The method of claim 1 in which the aluminum ingot is clad on both sides with zinc plate containing less than 0.02% by weight of metals having a melting point lower than zinc.

4. The method of claim 1 in which the zinc plate contains at least 99.99% by weight of zinc.

S. The method of claim 1 in which the zinc plate contains about 0.5% by Weight of copper.

6. The method of claim 1 in which the heating temperature before light rolling is within the range of from about 650 F. to less than 720 F.

7. The method of claim 1 in which the light rolling reductions are in the range of about 0.003 to about 0.05 inches per pass, and the number of light rolling passes is in the range of about 2 to about 40.

8. The method of claim 1 in which the aluminum ingot is a soft alloy of aluminum.

9. The method of claim 1 in which the thickness of the zinc plate is in the range of about 3% to about 10% of the total thickness of the composite before the first rolling operation.

10. The method of claim 1, in which the light rolling reductions are made in the absence of substantial lubrication.

11. A zinc clad aluminum article produced by the method of claim 1.

12. A zinc clad aluminum article produced by the method of claim 3.

References Cited in the file of this patent UNITED STATES PATENTS 1,554,097 Jordon Sept. 15, 1925 2,100,256 Larson Nov. 23, 1937 2,151,302 Scheller Mar. 21, 1939 2,443,870 Reynolds June 22, 1948 2,454,312 Fritzlen Nov. 23, 1948 2,707,323 Watson May 3, 1955 2,746,134 Drummond May 22, 1956 2,753,623 Boessenkool et al. July 10, 1956 2,850,798 Bowman et al. Sept. 9, 1958 2,879,587 Mushovic et al. Mar. 31, 1959 FOREIGN PATENTS 637,945 Great Britain May 31, 1950 762,817 Great Britain Dec. 5, 1956 

1. THE METHOD OF CLADDING ZINC TO AN ALUMINUM CORE WHICH COMPRISES HEATING A ZINC PLATE IN CONTACT WITH AN ALUMINUM INGOT TO A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 650*F. TO ABOUT 750*F., LIGHTLY ROLLING THE HEATED COMPOSITE TO ADHERE THE ZINC PLATE TO THE ALUMINUM INGOT, AND THEN HOT ROLLING THE ADHERED COMPOSITE UNDER PRESSURE TO REDUCE THE THICKNESS OF THE COMPOSITE AND TO BOND THE ZINC PLATE TO THE ALUMINUM INGOT, SAID ZINC PLATE CONTAINING NOT MORE THAN A MINOR PROPORTION BY WEIGHT OF ALLOYING METALS HAVING A MELTING POINT HIGHER THAN ZINC, LESS THAN ABOUT 1% OF METALS HAVING A MELTING POINT LOWER THAN ZINC, THE BALANCE BEING ZINC.
 11. A ZINC CLAD ALUMINUM ARTICLE PRODUCED BY THE METHOD OF CLAIM
 1. 